Electrical and mechanical maintenance

Electrical maintenance

The condition of the sawmill’s electrical equipment must be monitored regularly. The owner is responsible for the condition and safety of the production equipment.

In addition to qualified electricians, the condition of the electrical equipment can be monitored to some extent by the production staff at the sawmill. However, they must always receive sufficient training to perform these tasks.

Process scanners, measuring equipments and components

From the point of view of production, scanners related to the quality and protection of the product are a critical part of the sawing process.

The scanners within the sawing process can be categorised in the following way:

• Log sorting scanners
• Scanners related to loading, log rotation and measuring within the sawline and feeding processes
• Quality and process measurements within the sawline
• Edger scanner
• Scanners related to automation sorting within green sorting
• Moisture and temperature sensors in drying kilns
• Scanners related to automation sorting within quality sorting

Process automation and related equipment

The maintenance of electrical equipment includes parameter and software checks, testing, calibration, electrical measurements, replacing outdated and old components, cleaning and visual checks.

Below is a short description of some electrical sawmill equipment that has to be maintained and checked regularly:

1. Electrical equipment related to safety, such as safety logic systems, light curtains, safety relays and alarm and indicator devices. Safety devices must be checked before production start-up after a maintenance stoppage.
2. Process-related logic systems. Logic systems consist of the main system unit and the communication and I/O cards and control terminals connected to them. Logic systems are inspected 1–2 times a year. The condition of the factory bus should be checked at the same time.
3. Frequency converters. The maintenance of the frequency converters includes the replacement of ageing and worn components, parameter checks and visual checks. Frequency converters are usually serviced during annual maintenance.
4. The moisture and temperature sensors in drying kilns must be serviced regularly according to the instructions provided by the supplier.
5. Stampers. The servicing of the stampers mainly includes cleaning the device and stamper head. The frequency of servicing is determined through experience.
6. Metal detectors. The condition of metal detectors should be checked weekly. Metal detectors prevent more extensive damage to the machinery in the sawline or by-product line.

Sawmill power distribution and maintenance

In industrial settings, the medium voltage of 20kV, 10kV or 6kV is normally used and, using power network transformers, the voltage is converted into the 400V voltage between two phases used in low voltage networks.

The phase voltage in a low voltage network is 230V, which most people are familiar with. The sawmill’s power distribution equipment needs regular maintenance which is usually performed during annual maintenance.

Below is a summary of the most important power distribution-related devices and their maintenance intervals:

1. Power distribution transformers are inspected annually.
2. The maintenance of medium voltage switches, switchgear and isolating switches is carried out roughly every five years. The maintenance interval depends on the operating conditions and the manufacturer’s instructions.
3. The regular tests and inspections of discriminative protection are carried out within the intermediate and operating voltage systems every three years.
4. Power distribution support systems are inspected every six months. The actual maintenance on the auxiliary power system is carried out every 1–3 years on average depending on the technical structure of the system.
5. The power network compensators are inspected once a year.

Mechanical maintenance

Mechanical maintenance and repairs to the sawmill machinery mainly include machinery installations, aligning, servicing bearings, repairs on the machinery structure and preventive maintenance tasks.

The reasons for damage and breakage in the main drives, motors, gears and bearings usually include wrongly timed lubrication, over- or under-lubrication, use of the wrong lubricant, wrong or deficient installation tolerances and a heavier-than-expected load on bearings as the machinery’s operating mode, conditions or load changes.

Problems occurring with bearings during use can be predicted through regular condition monitoring.

Lubrication

The sawing process machinery is partly lubricated manually and partly through the central lubrication system.

1. Manual lubrication is divided into daily, weekly and monthly lubrication intervals. The challenge of manual lubrication is that not all lubrication points can be reached while the process machinery and equipment are running and some points have to be lubricated during stoppages.
2. The benefit of the central lubrication system is that the lubrication of machinery and equipment takes place while they are running and that the amount of lubricant used can be better optimised for each lubrication point. Moreover, there is less room for human error, such as forgetfulness or absence of the person who is supposed to carry out the lubrication, and so risks are reduced. Like all other systems, the central lubrication system requires regular checks and maintenance and, of course, filling up of the lubricant tank.

Measurement and alignment

Ensuring correct alignment after repairs and maintenance of the machinery is highly important. Alignment within the sawing process can be divided into two groups:

1. Aligning the positioning and centring devices of sawing machines
2. Aligning an individual machine

After major maintenance work has been performed on the sawline, the entire sawline must be aligned as the final maintenance task.

In addition to the main machinery, the positioning and centring devices must be checked. Either the production or maintenance department must document the alignment of the sawline in the maintenance system so that the measures performed can be checked after a test run in case the alignment is not correct.

The alignment of an individual machine or part of the machine at the installation stage is important. Sufficient accuracy of installation is a necessity for preventing premature damage on bearings, mechanical resonance, damage on axes or major breakage. Alignment affects motors, gears, belt drives, fans, pumps and axes.

Checks and servicing

The major checks and servicing of the machinery in the main line are performed during the annual maintenance stoppage. When servicing the main machinery in the sawline, such as debarkers, machinery in the bandsaw, circular saw and profiling lines, edger scanners and trimmers as well as packaging and tying machines, the sawmill’s own production and maintenance staff should be used as much as possible.

The maintenance of the drying kilns is mostly carried out during maintenance stoppages. The maintenance of the kiln process equipment focuses on fans, kiln radiators and heat exchangers that cannot be serviced during normal production. The main servicing tasks include lubrication of motors and fans, cleaning radiators and servicing equipment used for moving stick loads as well as repairs to structural elements. In addition to the maintenance staff, it is advisable to use the kiln process operators to perform kiln maintenance tasks.

By-product management at a sawmill involves belt, vibrating and redler conveyors, screws, elevators and rotary feeders as well as screens and chippers that are an important part of the process and need regular maintenance. More extensive and longer maintenance tasks are carried out during the annual maintenance stoppage.

Belt, vibrating and redler conveyors, screws, elevators and rotary feeders

Belt conveyor checks cover the belt itself and related devices such as:

1. support and return rollers
2. driving and turnabout rollers
3. belt brush
4. belt tensioning devices
5. drives

Belt conveyors must be inspected regularly taking into consideration their ambient and operating conditions.

Vibrating conveyor checks are less extensive and include electric drives, electrical cables and steel conveyor structures.

Redler conveyors are used to clean up the material that falls off other conveyors. Usually, problems with redler conveyors are a result of misuse.

Elevators are upright belt conveyors equipped with buckets. Elevators are mostly inspected the same way as belt conveyors.

Rotary feeders are used for feeding material during pneumatic transport such as moving sawdust. Regular servicing of rotary feeders is usually performed during annual maintenance stoppages.

Chains, chain wheels and guides, side transport skates and loaders

Sawline chains, chain wheels and guides, side transport skates and loaders must be inspected regularly.

The maintenance department can organise for the relevant operators to perform visual checks on these devices in a way that supports their overall maintenance. Regular inspections on them can be carried out during lubrication when lubrication has to be done manually and not when the process is running.

Screens and chippers

The maintenance of the sawmill’s by-product management screens and chippers happens during annual maintenance.

The maintenance of screens includes replacing the screen plates and monitoring the condition of the screen’s steel structures. The condition of the chippers at the by-product management section is monitored at the same time as the blades are replaced.

Machine automation

The sawing process machine includes automation, adjustable electrical drives, sensors, hydraulics and pneumatics.

The problems related to machine automation are challenging because there is really no comprehensive training available on tackling these problems but the relevant skills are usually learned through experience and practical training on the different sections.

Hydraulic

Sawmills make extensive use of hydraulic systems. It is important to have a safety lockout on drives that use hydraulics in order to ensure the safety of the staff.

Hydraulic systems may cause dangerous situations because there are great forces, pressures and potential residual energy involved.

The sawing process uses hydraulics in the main machinery that has changing blade positions and in various servo and proportional applications. However, expertise in hydraulics is often not enough; you also need cross-sectional teamwork in order to solve a problem. In addition to hydraulic components, the hydraulic adjustment system includes an automation or process control system, control cards and sensors.

Pneumatic

Pneumatics are used in the sawing process machine automation systems as much as hydraulics.

Pneumatics are mainly used in applications in the sawline and quality sorting that require less force. Pneumatic system applications include pressure wheels, loaders and centring devices related to the sawline and quality sorting.

The maintenance staff must be familiar with the components of the pneumatic system and the basic servicing measures. In addition to the basic pneumatic system components such as valves and pneumatic cylinders, the entire sawmill compressed air production equipment makes up an important part of the whole sawmill.

The operation of compressors and air dryers must be monitored and they must be serviced regularly by the maintenance staff in order for the system to perform faultlessly.

Building maintenance

The sawmill’s building-related technical maintenance tasks cover heating systems, water and sewage systems, air conditioning, refrigeration technology, building automation, power distribution, lighting and safety technology.

Often fewer preventive measures are taken to maintain these, which can cause unexpected problems that indirectly affect production.