Retos y desafíos de las industrias culturales y creativas

Measurement Technique

The track bushing is the most important component in the undercarriage to measure and interpret accurately.

To do this, three measurement methods are available, each using tools provided in the CTS tool kit.

You should refer to individual model family sections for specific recommenda- tion on which method to use because the second method described here, using depth gauge will record vertical position wear only.

1. Caliper Method

This method gives a direct reading of bushing diameter. With careful cleaning and proper technique it can yield the most accuracy, but is also the most susceptible to error if not properly measured. The most common errors using the caliper method are:

(A) Calipers Squeezed Too Tight — Calipers that are over tightened can be spread like a spring and will give too small of a reading.

(B) Calipers at Wrong Angle to Bushing Axis — Calipers that are set at an angle to the bushing will give an oversize measurement.

(C) Calipers Not Slid Back and Forth Across Position to be Measured — Calipers that are not passed back and forth over the maximum diameter of the bushing position being measured will give an undersize reading.

(D) Bushing not Cleaned Well Before Measurement — If the bushing surface is not cleaned the measurement taken will be oversized.

(E) Calipers Not Placed at Most Worn Portion of Bushing — If the caliper is located inboard or outboard of the minimum diameter along its length in a given wear position the reading will be undersized.

PRACTICE!

The best way to practice measuring bushing wear is with bushings removed from the track. You should be able to repeat the measurements made by yourself and others with an accuracy of ±.01" (± 0.25 mm).

2. Depth Gauge Method

The method for measuring the vertical position of bushings uses the same depth gauge used for links. This method is more free of the measurement technique errors encountered with the caliper, but may be subject to slight track link dimensional dif- ferences and track shoe bending. It is also subject to the same technique errors as link height measurements. These include: (a) parts not cleaned, (b) depth gauge base not positioned correctly with respect to bushing length and (c) depth gauge probe not forming a perpendicular or 90° angle with the shoe.

Disadvantages of the depth gauge method

(A) Cannot determine reverse or forward drive side wear, which is critical in most applications.

Advantages of the Depth Gauge Method

(A) Absolutely insures vertical position is being measured (unless measured at a point where track is bent).

(B) Averages diameter measurement of two adjacent bushings for greater accuracy.

(C) Backside of bushing can be measured after bushing turn (the importance of this will be explained in the next discussion).

3. Ultrasonic Wear Indicator Method

This method is the most accurate because it directly measures the most critical dimension, bushing wall thickness. It also can be used to accurately measure the backside of bushings after a bushing turn.

Measure the bushing wall thickness by slowly sliding the probe around the reverse, vertical, and forward drive sides. Use the smallest dimension to determine percent worn.

Sealed and Lubricated Track

Bushing Wear

Measurement Positions

Refer to individual product sections for specific guidelines.

Wear Limits — Greater and Lesser

Wear limits for Sealed and Lubricated Track bushings are determined by remaining crack resistance strength. Two percent worn columns titled “lesser allowable wear” and

“greater allowable wear” are provided in bushing wear charts. At 100 percent worn, the lesser allowable wear column pro- vides more bushing wall thickness than the greater allowable wear column. Note, for example, in the wear charts under the ultra- sonic measurements, the bushing wall is always thicker, and thus more crack resis- tant, on the lesser allowable wear column than on the greater.

The selection of the optimum allowable wear column will maximize the link and bushing life while preventing bushing cracking. The “optimum” percent worn column depends on the relative bushing crack resistance required in your situation. The amount of required crack resistance depends on several factors including sprocket position (high or low), underfoot conditions, bushing projected life, and application. Refer to the management section in front of each product section for the criteria to use in selecting which allow- able wear chart to use.

Wear Charts

The expected wear rate through the allow- able wear limit is determined from several tests. These rates are built into the wear charts so that accurate projection to 100 per- cent worn and 120 percent can be made assuming uniform abrasive, impact and other conditions will continue. The built-in bushing wear rate after the hardened case has been completely worn through is approxi- mately 2 times the rate expected in the hard- ened case depth.

Like with most other components, projec- tions made to the service points based on less than 30 percent worn will not be accurate. The wear charts provide the percent worn equivalent for those mea- surements less than 30 percent only for projecting re-visit or re-measurement points. The bushing is the most likely component to use for this re-measurement projection.

Sealed and Lubricated Track vs Sealed Track Effects

Due to expected absence of internal wear the Sealed and Lubricated Track bushing should have its most worn position on or very near the vertical position. Sealed Track is expected to have either forward or reverse position as the most critical position. The Sealed and Lubricated Track bushing also has fewer wear positions to analyze.

The expected life of the Sealed and Lubri- cated Track bushing is approximately 50 per- cent more than the Sealed Track bushing when compared to either high or low impact service limits.

These increases depend on the following: 1. Degree of internal wear that contri-

buted to the external wear on the Sealed Track bushing.

2. Properly adjusted track.

3. Absence of very severe packing. 4. Similar working conditions.

Sealed and Lubricated Track Bushing Turnability

The Sealed and Lubricated Track bushing should be turned based on the guidelines in following sections entirely devoted to specific model families.

The bushing may be expected to provide life after turn wear, equal to or exceeding the wear life potential of the first or front side prior to the turn.

Sealed and Lubricated Track bushings can be successfully turned wet if there are no cracks through the bushing wall at turn time and seal wear life guidelines have not, or will not, be exceeded.

Sealed and Lubricated Track bushings may be successfully turned dry, (with or without internal wear at turn time) as long as there are no cracks through the bushing wall and internal wear does not exceed Sealed Track service limits.

Life after dry turn cannot be expressed as a percent of wet life before turn. It will most closely approximate life after turn of Sealed Track in hours, not percent.

How to Interpret Sealed