Square Baler Loose Bales: Density Troubleshooting Guide

The bale chamber walls are lined with replaceable wear strips that maintain the correct internal dimensions. As these strips wear, the effective chamber cross-section increases — the same density setting now produces a bale with more physical size but less material per unit volume, which exits looser and lighter than before. Wear strip wear is progressive and gradual, which is why operators often do not notice the problem until bale weight has fallen by 10–15%.

Measure the chamber internal width and height at three points along the chamber length and compare to the specification in the operator manual. If any measurement exceeds the maximum worn dimension, replace the wear strips. This is a standard pre-season maintenance item — check wear strips annually and replace as a set when any one strip is at the wear limit. After replacement, run 10 calibration bales and adjust the density setting to achieve the target bale weight, as the new strips reduce the effective chamber size and require a lower tension setting to achieve the same output weight.

The chamber door resistance is generated by either a mechanical spring system or a hydraulic cylinder depending on model. Springs lose their rated load over time from metal fatigue — a spring that correctly resisted 300kg door force when new may only resist 200kg after 8–10 seasons of compression cycling. A hydraulic system loses pressure resistance from seal wear or fluid contamination. In both cases, the density adjustment mechanism is still functioning correctly but the maximum achievable resistance has decreased below the original specification.

Test spring load by measuring the spring free length and comparing to the specification. A spring that has shortened by more than 5% of its original free length has lost significant load capacity and should be replaced. For hydraulic systems, check the system pressure at the cylinder inlet with a pressure gauge at maximum density setting and compare to the specification. If below specification, check for seal leaks and fluid condition before replacing cylinders. Replace springs or cylinder seals as indicated — this is a precision component and using a spring of incorrect rating is not acceptable.

Bale density in a square baler is partly determined by the kinetic energy of the plunger at peak compression — a plunger at 540rpm strikes the accumulated crop with significantly more impact energy than one at 480rpm. Below-rated PTO speed reduces the compression force actually delivered per stroke. An underpowered tractor that cannot maintain 540rpm PTO under the combined plunger, feeder and pickup load produces consistently lighter bales than the same machine at rated speed, regardless of the spring or hydraulic tension setting.

Monitor PTO speed via tractor engine RPM — at what engine speed does the PTO reach 540rpm on your tractor? Run at that engine speed or above throughout the session. If the tractor cannot maintain rated PTO speed during peak compression loads, reduce forward speed until the engine recovers to rated speed, or reduce the density setting to lower the plunger load per stroke. If PTO speed is consistently below 530rpm at any practical forward speed, the tractor may be undersized for the baler or the windrow density — consider the correct HP match for each 9YF model in the product specifications.

Each plunger stroke compresses a fixed volume of chamber space. The amount of crop compressed on each stroke depends on how much material the feeder delivers to the inlet between strokes — which depends on the windrow density at that point. A non-uniform windrow — one that was raked unevenly, received extra material from a nearby windrow overlap, or has variable crop yield across the field — delivers variable material volumes to the inlet and therefore produces variable bale weights even when the machine settings are constant.

Improve windrow uniformity in the raking pass: maintain consistent tractor speed when raking, avoid merging windrows unless you also reduce forward baling speed for that section, and do not rake over areas where windrows have already been disturbed by previous passes. A windrow width variability of less than 20% across the field will produce bale weight variation of less than 15% from the same machine settings. If the field inherently has high yield variation, consider raking twice in crossing directions to average out the density before baling.

Pickup tines that are bent, broken or worn below their effective working length recover less crop from the windrow per pass than a full-complement, correctly profiled pickup. A spring-tooth pickup with 15% of tines bent or missing delivers approximately 85% of the material rate of a fully-functional pickup — producing bales that are consistently 10–15% lighter than expected at the same density setting and forward speed, even when the machine is otherwise in good condition.

Walk the machine after the previous session and inspect each tine. Bent spring tines can be straightened once but should be replaced if bent a second time — repeated bending indicates the tine is fatigued. Missing tines create gaps that leave a stripe of uncollected crop across the windrow width. Replace all missing, bent or shortened tines as a set — replacing individual tines of different ages creates an uneven pickup face that delivers non-uniform material rates. Tine replacement is inexpensive and is the correct action whenever visible crop is being left on the ground.

High-moisture hay compresses very effectively at baling — the water in the stems acts as a lubricant that allows stems to slide past each other into a tight pack. The bale exits firm and apparently well-compressed. As the moisture evaporates in storage, the stems return toward their original dimensions and the bale loses the lubrication effect — the apparent volume increases and the bale feels loose, sometimes falling apart at the ends. This is not a machine fault; it is a crop condition problem.

Measure windrow core moisture with a probe meter before baling. For small square bales in covered storage, bale at 14–17% moisture maximum — above this range, the post-baling relaxation effect becomes significant. If weather forced baling at higher moisture, store bales in a single layer with airflow for 48–72 hours before stacking — this allows partial moisture equalisation before the stack creates insulating pressure. Do not stack high-moisture bales immediately after baling; the combined heat and pressure accelerates loosening and creates fire risk above 70°C internal temperature.

The star wheel measures bale length by contact with the forming bale surface and triggers the knotters when the set length is reached. A worn star wheel with flattened contact points may slip on smooth or polished bale surfaces rather than rotating with the bale movement — it under-counts the bale length and triggers the knotters late, producing bales longer than the set length. Conversely, a worn trip arm that triggers too easily produces shorter bales. Both result in inconsistent bale weight even when windrow density and machine settings are constant.

Measure 10 consecutive bales with a tape measure. If bale length variation exceeds 50mm (approximately 10% of standard 460mm cross-section bale length), the star wheel and trip mechanism need inspection. Check the star wheel tine tips for wear and flattening — worn tips should be replaced. Check the trip arm spring for fatigue and the cam latch for wear. Lubricate the star wheel bearing as specified in the operator manual — a stiff bearing causes the wheel to slip rather than rotate, mimicking the same symptom as worn tine tips. This is a service item included in the annual pre-season checklist.

As alfalfa and grass crops mature through the season, stem diameter increases and cell wall lignification increases. Mature stems have higher bending stiffness than young stems and do not compress into the same tight packing as first-cut material. A chamber that compresses first-cut alfalfa to 24kg per 460mm bale may only compress third-cut alfalfa to 18–20kg at the same spring setting because the mature stems spring back more aggressively against the plunger. This is a crop property, not a machine fault.

Increase the density tension setting when switching to later cuttings or more mature material. Run 10 calibration bales after each cutting start, weigh them, and adjust the tension to achieve the target weight for that crop stage. For operations where consistent bale weight is critical across all cuts, the 9YF-2200S with its integrated shredder provides a measurable density advantage with mature stems — the shredder breaks cell walls before compression, allowing late-cut material to pack more uniformly than unshredded long stems. This is the primary agronomic argument for the shredder model in multi-cut alfalfa operations.